Surface area of an object
There is an addon called the 3D Print Toolbox which is included in Blender that has this function. It can be found in the addons list in the User Preferences. Once you have the addon enabled, the new options will be in a new tab in the toolbar. At the top there is an area button that will calculate the surface area. I'm assuming your using centimeters as your units. If not, go to the scene tab, and in the Units panel switch the preset to centimeters. You may have to adjust the scale based on whatever you were working on. By default, centimeters are 100 times smaller than the default Blender units.

EDIT: IF you are working with different units already and don't want to mess things up you will have to do the conversion manually from whatever unit you are in, as the output units are always in whatever units the scene is using. There is probably a way to get around this by modifying the addon if you are so inclined though.